Many studies tested the association between numerical magnitude processing and mathematics achievement, results differ depending on the number format used. For symbolic numbers (digits), data are consistent and robust across studies and populations: weak performance correlates with low math achievement and dyscalculia. For non-symbolic formats (dots), many conflicting findings have been reported. These inconsistencies might be explained by methodological issues. Alternatively, it might be that the processes measured by non-symbolic tasks are not critical for school-relevant mathematics. A few neuroimaging studies revealed that brain activation during number comparison correlates with the children’s mathematics achievement level, but the consistency of such relationships for symbolic and non-symbolic processing is unclear. These neurocognitive data provide ground for educational interventions, which seem to have positive effects on children's numerical development in (a)typical populations.